The present invention refers to a packing assembly for sealing a machine shaft rotating and/or oscillating in a machine housing, comprising a packing accommodation member adapted to be floatingly arranged on the machine shaft and a ball joint assembly adapted to support the packing accommodation member such as to prevent rotation and/or axial motion thereof with respect to the machine housing.
Such a packing assembly can be used, for example, for sealing the interior of the working chamber of a processing machine having a rotating and/or oscillating shaft, particularly machines and apparatuses used in the chemical, plastic, food, pharmaceutical and cosmetics industries for mixing, kneading, plasticizing and homogenizing a product.
A fundamental problem in the field of sealing a working chamber having therein a rotating shaft may be seen in the fact that such shaft always show, to a more or less extent, run out of true, pendulum motion and dynamic unbalance. It is understood that these errors have a negative influence on the sealing properties of the packing assemblies discussed herein, because a radially directed relative motion of the shaft with respect to the sealing packets of the packing assembly occurs, with the result that the sealing packets are heavily stressed. Particularly, pendulum motions have a pronounced negative effect on the sealing characteristics and the service life of such packing assemblies.
The above discussed problems are particularly accentuated in the case of big, heavy and greatly stressed shafts, particularly if they not only rotate, but simultaneously perform an oscillating movement.
In order to circumvent the above mentioned problems, so-called floating shaft sealing assemblies have been used in the past, in which a sealing packet accommodation member is floatingly received on the machine shaft. A problem to be solved in connection with these floating sealing assemblies is how to support such assemblies, ensuring a corresponding degree of freedom to allow for pendulum and wobbling motions of the shaft. Up to now, usually elastic support elements have been used which allow both for radial deflection and pendulum motion of the machine shaft. However, experience has shown that the service life of such elastic support elements is very limited, particularly if they are under great thermal stress. Moreover, they can bear only comparatively small torque forces and show relatively high reset forces, further impairing the service life of the sealing packets.
The patent publication DE 1,214,199 discloses an apparatus for mounting vertically extending rotating shafts. This apparatus comprises a packing gland floatingly arranged on the shaft, sealing the shaft with regard to the housing in cooperation with a movable folding bellows, a stuffing box and a stuffing box gland.
The patent publication FR 2,450,393 discloses a sealing assembly for sealing shaft members extending through the wall of a housing. The sealing assembly includes a stuffing box floatingly arranged between the housing and the shaft. As a means for preventing rotation of the stuffing box, a screw is provided which is fixed to the housing and engages a recess in the stuffing box. A waterproof seal between the housing wall and the stuffing box is ensured by a bellows sealing member, allowing for relative movement between the floating stuffing box and the housing.
The patent publication GB 684,373 discloses a reaction vessel having a rotating mixing and stirring shaft. For the sake of sealing the shaft extending through the vessel wall, both sides of the wall of the reaction vessel comprise sealing members in the form of stuffing boxes. A portion of the housing of the stuffing box shows a spherical surface which is supported by means of an annular element, having a spherical surface as well and being welded to the wall of the reaction vessel. For stationary fixing the stuffing box, a retainer cap is provided which is bolted to the housing of the reaction vessel. The retaining cap is provided with a spherical interior surface located at its upper end, in which the stuffing box housing, having a spherically shaped surface portion as well, is supported. Such a design allows for pendulum motions of the shaft with regard to the reaction vessel. For filling a space between the stuffing box housing and the retaining cap, pipes extending through the retaining cap are provided.
Finally, the patent publication WO 94 21944 discloses a self-aligning shaft bearing provided with a stuffing box. The shaft bearing comprises a bearing housing defining in its interior a bearing chamber. The bearing housing comprises an essentially tube-shaped base member and a closure element bolted to the base member. The bearing chamber is located between the outermost end of the base member and the interior of the closure element. Moreover, that shaft bearing comprises a guiding assembly comprising a tube-shaped inner element through which the shaft extends. The inner element is provided with two radially extending flange members which are supported by a bearing element located in the corresponding bearing chamber. This shaft bearing is suitable both for rotating and oscillating movements of the shaft.
With the above discussed prior art in mind, it is an object of the present invention to provide a packing assembly for sealing a machine shaft rotating and/or oscillating in a machine housing, having a ball joint assembly for supporting a packing accommodation member adapted to be floatingly arranged on the machine shaft, which is of simple design and can be manufactured at low costs, whose service life nevertheless is considerably extended and which ensures a reliable and long-time stable sealing of the machine shaft.
In order to meet this and other objects, the present invention provides a packing assembly for sealing a machine shaft rotating and/or oscillating in a machine that comprises a packing accommodation member adapted to be floatingly arranged on the machine shaft and a ball joint assembly adapted to support the packing accommodation member such as to prevent rotation and/or axial motion with respect to the machine housing.
The ball joint assembly includes a ball member provided with a central bore and a socket member for rotatably receiving the ball member. The packing assembly further comprises a guiding element having a guiding portion projecting into the central bore provided in the ball member and adapted to translatory guide the ball member along the central longitudinal axis of the central bore in the ball member. Thereby, the central longitudinal axis of the bore in the ball member runs essentially perpendicular to the central longitudinal axis of the machine shaft.
The proposed packing assembly avoids to a farthest extent both translatory relative motions between packing assembly and machine shaft as well as relative pendulum motions between packing assembly and machine shaft. Moreover, the herein disclosed ball joint assembly is essentially maintenance-free. Pendulum motions of the shaft and the sealing packet accommodation member floatingly received thereon, respectively, are absorbed by the ball joint assembly and transformed into lateral motions. The ball joint assembly, moreover, is of simple design, can be manufactured at low costs and has an extended service life. Furthermore, it exhibits comparatively low reset forces.